Mark A. Norell, who heads the museum’s paleontology division, was flipping through letters and packages in his office atop one of the museum’s turrets when he noticed an alarming curiosity in a catalog of scheduled auctions in Manhattan: a perfectly assembled Tyrannosaurus bataar skeleton.

Mr. Norell believed there was almost no chance that the 24-foot-long, 8-foot-tall fossil had been legally removed from Mongolia, the only country where that type has been found. On May 17, three days before the auction, he wrote an open letter that was posted to listservs frequented by paleontologists.

“As someone who is intimately familiar with these faunas, these specimens were undoubtedly looted from Mongolia,” the letter said.

Thus began a whirlwind tale that came to involve the president of Mongolia; a lawyer in Houston; paleontologists and the United States attorney in Manhattan, Preet Bharara, who on Monday filed a civil complaint seeking forfeiture of the skeleton and requesting its return to Mongolia.

The chaos surrounding Lot 49315 at a building called Center 548 in Chelsea was certainly uncommon, and not only because the item in question was not a painting, but an “incredible, complete skeleton, painstakingly excavated and prepared,” according to the catalog from Heritage Auctions.

The catalog led Mr. Norell to compose his letter, which landed on the desk of Tsakhia Elbegdorj, the president of Mongolia. The remains for Tyrannosaurus bataar, which lived 70 million years ago, were first discovered in 1946 during a joint Soviet-Mongolian expedition to the Gobi Desert. Under Mongolian law, fossils are the property of its government and are illegal to export.

President Elbegdorj was familiar with a Houston lawyer, Robert Painter, and called late Friday asking for help.

Photo

The government of Mongolia says that this Tyrannosaurus bataar is its property and should be returned.Credit
U.S Attorney Office for the Southern District of New York, via Associated Press

The next morning, Mr. Painter, who had met the president while representing United States investors in Mongolian mining ventures, found a federal judge in Texas to sign a temporary restraining order at his house on May 19, a Saturday morning.

Mr. Painter said he sent the order electronically to Heritage and then flew to New York to make sure the auction did not proceed. He worried that once the fossil was sold, it would disappear forever.

He arrived to find the fossil being showcased in the auction room.

“The auctioneer said the sale would proceed contingent on the outcome of a court case,” Mr. Painter said in an interview.

Mr. Painter said he called the judge, Carlos Cortez, on his cellphone.

“I stood up, raised my cellphone, and said, ‘I have the judge, and he’s ready to explain to you how this violates the court’s order,’ ” Mr. Painter said.

Mr. Painter said that he was politely ushered to the side of the room and that the auction proceeded. The fossil was purchased by an anonymous buyer, via telephone, for $1,052,500.

The next day, Heritage agreed to halt the sale pending the outcome of an investigation.

The federal civil complaint says that the fossil had been imported from Great Britain to Gainesville, Fla., in March 2010 by a company owned by a man who describes himself as a “commercial paleontologist.” The complaint says that documents presented to customs officials misstated the skeleton’s country of origin as Great Britain, misstated its value as $15,000, and incorrectly described the bones.

A spokesman for Heritage Auctions issued a brief statement from Jim Halperin, the company’s co-chairman, saying it believed that the seller had “purchased fossils in good faith, then spent a year of his life and considerable expense identifying, restoring, mounting and preparing” the skeleton.

Since the auction, the skeleton has been housed in an art storage site in the city. On Tuesday a federal judge in Manhattan, P. Kevin Castel, signed an order for federal law enforcement officers to take the skeleton into custody, Mr. Painter said.

The federal complaint also mentions the opinion of Mr. Norell and Philip Currie, a professor of dinosaur paleobiology at the University of Alberta, that the skeleton had been removed from Mongolia by poachers within the last decade. The skeleton was missing claws, toes and teeth, which are prime targets of poachers, and the fresh breaks of bones indicate it had been removed in recent years, they found.

A version of this article appears in print on June 20, 2012, on page A21 of the New York edition with the headline: Sale of $1 Million Dinosaur Skeleton Is Halted After Paleontologist Questions Origin. Order Reprints|Today's Paper|Subscribe